The present invention relates to an exhaust gas recirculation system, and more particularly to a method and system for controlling an exhaust gas recirculation system.
There is a growing concern over the long-term effects of Nitrogen Oxides (hereinafter NOx) and Carbon Dioxide (hereinafter “CO2”) and Sulfur Oxides (SOx) emissions on the environment. The allowable levels of emissions that may be emitted by a turbomachine, such as a gas turbine, are heavily regulated. Operators of turbomachines desire methods of reducing the levels of NOx, CO2, and SOx emitted.
Significant amounts of condensable vapors exist in the exhaust gas stream. These vapors usually contain a variety of constituents such as water, acids, aldehydes, hydrocarbons, sulfur oxides, and chlorine compounds. Left untreated, these constituents will accelerate corrosion and fouling of the internal components if allowed to enter the gas turbine.
Exhaust gas recirculation (EGR) generally involves recirculating a portion of the emitted exhaust through an inlet portion of the turbomachine. The exhaust is then mixed with the incoming airflow prior to combustion. The EGR process facilitates the removal and sequestration of concentrated CO2, and also reduces the NOx and SOx emission levels.
There are a few concerns with the currently known EGR systems. Impurities and moisture within the exhaust gas prevent utilizing a simple re-circulating loop to reduce the generation of emissions, such as SOx emissions. Turbine fouling, corrosion, and accelerated wear of internal turbomachine components would result from introducing the exhaust gas directly to an inlet portion of the turbomachine. As a result, the diverted exhaust gas should be treated prior to blending with the inlet air.
For the foregoing reasons, there is a need for a method and system for controlling an EGR system. The method and system should allow for the EGR system to reduce the level and/or concentration of emissions within the recirculated exhaust gas stream.